Junk often refers to poker hands which have a low percentage of winning pots, do not play well post flop, and are typically unsuited in nature. These "junk" hands can be defined different but overall fall into the bottom 15-20% of hand strengths. Junk hands would include hands such as:
K2-K5o Q2o - Q6o J2o-J6o T6o-T2o 94o-92o 84o-82o 64-62o and finally the worst hand of all hands Seven Deuce offsuit. 72o is the worst possible hand because it can not make a straight or a flush by using both of its hole cards and its pair value is also quite poor.